Optimum Ductility Research Articles

Microstructure Characteristic and Mechanical Properties of Copper Influenced Grey Cast Iron

Grey cast iron (GCI) is characterized by brittleness, making it unsuitable for use in applications requiring high impact loading. Hence, efforts were made in this study to produce GCI with improved mechanical properties by addition of copper. Four samples were produced, the first sample was not alloyed (control), and the second, third and fourth were alloyed with 1.4wt.%Cu, 1.8wt.%Cu and 2.2wt.%Cu respectively. The samples were characterized using scanning electron microscope with EDS, and tested in tensile, hardness and impact. From the results, silicon contents of the alloyed samples are high relative to the control sample. The control and 2.2wt.%Cu alloyed samples are hypereutectic with carbon equivalent values (CEVs) of 4.391% and 4.200% respectively, while the 1.4wt.%Cu and 1.8wt.%Cu alloyed samples are hypoeutectic with CEVs of 3.940% and 3.600% respectively. The control sample is characterized by long graphite flakes, which are uniformly distributed within ferritic - pearlitic matrix. Graphite flakes of the 1.4 wt.% Cu and 1.8 wt.% Cu alloyed samples are uniformly distributed within pearlitic - ferritic matrix, while graphite flakes of the 2.2wt.%Cu alloyed sample are uniformly distributed within ferritic-pearlitic. Average graphite flake length of the control sample is high as compared to the copper alloyed samples, while graphite flake count of the control sample is low relative to the copper alloyed samples. Tensile strength characteristics of the copper alloyed samples are superior to the control sample. Optimum tensile strength characteristics (165.9 Nm2) was obtained at 1.4wt.%Cu. Ductile characteristic of the of control the sample is superior to ductile characteristics of the copper alloyed samples. Optimum ductility characteristic (3.82%) was obtained at 2.2 wt. %Cu. Hardness characteristics of the copper alloyed samples are superior to hardness characteristic of the control sample. Optimum hardness characteristics (61 HRB) was obtained at 1.4wt.%Cu. Impact strength characteristic of the control sample is low relative to impact strength characteristics of the copper alloyed samples. Optimum impact strength characteristics (78.93 KJ/m2) was obtained at 2.2wt.%Cu.

Fracture behavior of a rapidly solidified thin-strip continuous cast AA5182 Al-Mg alloy with the Portevin-Le Chatelier effect under varying strain rates

This study investigates the strain-rate triggered PLC effect and fracture behavior of a rapidly solidified thin strip (TS) cast AA5182 alloy in comparison with those of direct chill (DC) counterparts. Higher cooling rates obtained via TS casting suppress the formation of phases in Al-Mg alloys and significantly enhance the matrix solute supersaturation beyond the equilibrium level, thereby impacting the interaction dynamics of mobile dislocations and solute atoms. This in turn affects the evolution of typical stress fluctuations in Al-Mg alloys, referred to as the Portevin-Le Chatelier (PLC) effect, occurring in specific strain rate-temperature domains, i.e., with type and characteristics dependent upon the microstructure. Tensile testing demonstrated a strain-rate dependent PLC effect, also aligning with the ductility trend in both negative and positive strain-rate sensitivity domains. The characteristics of PLC bands, as well as the magnitude of stress fluctuations, were shown to evolve with strain rate, facilitating distinct fracture mechanisms. In particular, the TS sample exhibited a higher strain rate sensitivity of the fracture mechanisms and PLC band characteristics and, thus, a narrower range of deformation rates for optimum ductility (attributed to increased solute in the matrix). Controlling the deformation rate to favor predominantly Type-B serrations and ensuring their stability with minimal fluctuations was shown to postpone necking and prevent material failure. The significance of rate sensitivity in alloys with reduced microsegregation is emphasized, suggesting the need for further exploration of mechanical properties.

Microstructure Characteristics, Mechanical and Corrosion Properties of Copper Alloyed Hypo-Eutectic Grey Cast Iron

In this study, influence of varied copper addition on the mechanical properties and corrosion characteristics of grey cast iron (GCI) was investigated. As-cast unalloyed and 0.035 wt. %, 0.65 wt. % 0.85 wt. % and 1.18 wt. % copper alloyed GCI samples were produced using rotary furnace. Chemical compositions of the samples were determined by Optical Emission Spectroscopy using ARL QuantoDeskSpectro analysis machine. Tensile and hardness measurements were made using INSTRON tensile testing machine- model 3369 and Universal Rockwell hardness testenr- model 8187LKV respectively. Samples’ characterization was done using Philips SEM (XL30 TMP). And electrochemical measurement was determined using AUTOLAB PGSTAT 204N instrument. From the results, the as-cast unalloyed, 0.035 wt. % and 0.85 wt. % and 1.18 wt. % Cu alloyed GCI samples revealed lamella graphite in pearlite matrix, short flake graphite in pearlitic-ferrritic matrix, Type A flake graphite in pearlitic-ferritic matrix and long flake graphite in ferritic-pearlitic matrix respectively. Tensile, hardness and elongation properties of the copper GCI samples ranked superior over the as-cast unalloyed GCI sample. Optimum tensile value 158.26 N/mm2 and hardness value 447.4 HRC were revealed by the 0.85 wt. % Cu, and optimum ductility value of 2.79% was revealed by the 1.18 wt. % Cu alloyed GCI sample. In general, copper alloyed GCI samples showed better corrosion resistance relative to the as-cast unalloyed GCI sample. The copper alloyed GCI samples showed better corrosion resistance relative as compared to the as-cast unalloyed GCI sample. Least corrosion rate of 0.0011297 mm/yr with polarization resistance of 174.58 Ω was revealed by the 0.85 wt. % Cu alloyed GCI sample. Hence, it is most suitable in application requiring high to moderate strength is marine environment.

Experimental Study on the Dip Angle Effect of Layered Cemented Fillers: A Sandblasting Treatment Applied to Mine Filling

In order to study the effect of interlayer dip angle on the mechanical properties of tail sand cemented filler and to improve the deterioration of the mechanical properties of the filler caused by delamination, this study introduces the sandblasting method for treating the interface between old and new concretes in concrete science. Two types of delamination, natural delamination and sandblasting delamination, were produced for the tailing sand cemented filler specimens, and the interlayer dip angles were set to 0°, 10°, 20°, and 30°, respectively. Uniaxial compression tests were conducted at maintenance ages of 3 d, 7 d, 14 d, and 28 d, and damage models were established. The results show that (1) the uniaxial compressive strength and modulus of elasticity of the naturally delaminated specimens decrease and then increase with the increase of interlayer dip angle, and reach the lowest at the interlayer dip angle of about 20°. The uniaxial compressive strength and modulus of elasticity of sandblasted delaminated specimens with interlayer dip angle, not more than 20°, can bring positive gains in uniaxial compressive strength and modulus of elasticity, and the stable gains at high age can reach 6.4% and 39.7%, respectively. (2) The post-peak ductility of the two-layered types of specimens increases and then decreases with the increase of the dip angle between layers and reaches the optimum ductility at about 20° of dip angle. (3) The damage of the delaminated filling body is mainly in the form of tensile damage and conjugate shear damage, and the sandblasting treatment can improve the force transmission mode on the delamination surface. (4) Based on the damage evolution of the soil body with Weibull distribution, the damage instantiation model of the layered colluvial filler is constructed, which has high reliability for different interlayer dip angles. Accordingly, the findings of this study demonstrate that the addition of sandblasting can significantly reduce the degradation of the mechanical properties of the tailing sand cemented fill brought on by delamination at a slow dip angle (below 20°), and offer a helpful damage ontology model for use in engineering practice.

Effect of fiber constituent in matrix on cyclic behavior of PVA-Steel hybrid Fiber-Reinforced cementitious composites columns with mild steel rebar

This study aims to investigate the seismic performance of reinforced cementitious composites columns strengthen by different fibers addition strategies. Six fiber-reinforced cementitious composites (FRCCs) columns are tested under reversed cyclic loading to explore the impact of Cementitious composites with Polyvinyl alcohol (PVA) fibers and hybrid cementitious composites simultaneously containing PVA and steel (ST) fibers on hysteresis behavior of the columns, in which fiber dosage and the combination proportion of PVA and ST fibers in composites are focused. The structural performance of the tested columns is evaluated based on the characteristics of the cracking behavior, ductility, load-carrying capacity, stiffness degradation, energy-dissipation capacity, and strain profiles of the reinforcements. The test results indicate that columns with 2 % vol. fibers compared to those including 1 % vol. fibers presented the better performance in terms of cracking behavior, ductility, and energy dissipation. The cementitious composites reinforced by 1.5 % vol. PVA + 0.5% vol. ST fibers contributes to the column characterized by optimum ductility in comparison to all columns with the other fibers. The highest energy dissipation capacity among the tested columns is observed in the case of the composites with 1 % vol. PVA + 1 % vol. ST fibers. The column with 0.5 % vol. PVA + 0.5 % vol. ST fibers manifests the better load carrying capacity over the rest of columns.

The Effect of ECAP Processing Conditions on Microstructural Evolution and Mechanical Properties of Pure Magnesium-Experimental, Mathematical Empirical and Response Surface Approach.

In this study, a quantitative evaluation approach was used to investigate how certain ECAP processing parameters affect the microstructural evolution, Vicker’s microhardness values and tensile properties of pure Mg. The ECAP processing parameters were number of passes, ECAP die channel angle and processing route type. The response surface methodology (RSM) technique was used to design 16 runs of the experiment using Stat-Ease design expert software. Billets of pure Mg were processed up to four passes of routes Bc, A and C at 225 °C. Two ECAP dies were used with internal channel angles of 90° and 120°. Experimental findings were used to establish empirical models to assess the influence of the ECAP processing parameters on grain size and mechanical properties of ECAPed billets. The established relationships were examined and validated for their adequacy and significance using ANOVA as well as several statistical criteria. Response surface plots and contour graphs were established to offer better understanding of the intended relationships. In addition, the optimum processing parameters for grain size, hardness values and tensile properties were defined. Both experimental results and the theoretical model revealed that route Bc is the most effective route in grain refining. The experimental findings showed that four passes of route Bc through the die channel angle 90° revealed a significant reduction in the grain size by 86% compared to the as-annealed counterparts. Similar to the grain size refining, four-passes processing through the ECAP die with an internal channel angle of 90° leads to improved Vicker’s microhardness values. Additionally, four passes of route Bc using the 90° die angle recorded a significant HV increase at the edge and central areas by 112% and 78%, respectively, compared to the as-annealed counterpart. On the other hand, according to the optimization findings, two passes of route Bc using a die angle of 120° resulted in the best ultimate tensile strength for pure Mg, whereas four passes of route Bc revealed the optimum ductility at fracture.

Role of thermal history on atomic structure and ductility of ion-irradiated metallic glasses

Maximizing the structural rejuvenation and ductility is one of the most heated debates in the field of metallic glasses (MGs). In this work, molecular dynamics simulation was implemented to model the ion irradiation effects on the Cu60Zr40 MG with different thermal histories and varied structural heterogeneities. The initial results indicated that the performance of an annealing–quench treatment on the MG induces the atomic configurations with different heterogeneities and potential energy values. The subsequent ion irradiation process also demonstrated that an optimized atomic structure was occurred for achieving maximum rejuvenation and ductility in the CuZr glassy alloy. It was unveiled that the intermediate initial heterogeneity provides an efficient pathway for maximizing the atomic rearrangements under the ion irradiation. It was also suggested that the medium population of Cu-centered clusters in the initial state facilitated the atomic rearrangements during the ion irradiation process. The structural characteristics and atomic reconfigurations for attaining the optimum ductility is discussed in details.

Effects of cellulose nanofiber content on impact properties of carbon fiber reinforced epoxy composites with the cellulose nanofiber dispersion layer

Cellulose nanofibers (CNFs) are environmentally friendly materials with a high specific strength. To enhance the impact properties of the carbon fiber reinforced plastics (CFRPs), a method for inserting a CNF dispersion layer between prepregs was developed. By using an aqueous solution of epoxy resin, the hydrophobic treatment of CNF became unnecessary. In this study, CFRP with CNF dispersion layers was fabricated with different CNF content. The impact energy absorbed by the CFRP specimen was increased with the increasing CNF content, and the Charpy impact value increased up to a maximum of 21% by the CNF dispersion layers. Highlights Carbon fiber reinforced plastics (CFRPs) specimens with the cellulose nanofiber (CNF) dispersion layer were fabricated. The specimens were fabricated by varying the content of CNF. Impact energy absorbed by the CFRP specimen was increased with increased CNF content. Charpy impact value increased up to 21%; optimum ductility index value was clarified.

The Durability of High‐Strength Concrete Containing Waste Tire Steel Fiber and Coal Fly Ash

The demands for high‐strength concrete (HSC) have been increasing rapidly in the construction industry due to the requirements of thin and durable structural elements. HSC is highly brittle. Therefore, to augment its ductility behavior, expensive fibers are used. These negative drawbacks of HSC can be controlled by incorporating waste materials into its manufacturing instead of conventional ones. Therefore, this study assessed the performance of HSC produced with different quantities of waste tire steel fiber (WSF) and fly ash (FA). WSF was used at two doses, namely, 0.5% and 1%, by volume in HSC, with low‐to‐medium volumes of FA, that is, 10%–35%. The studied durability parameters included rapid chloride permeability (RCP) and chloride penetration depth (CPD) by immersion method (28 and 120 days) and acid attack resistance (AAR) (28 and 120 days). Various basic mechanical properties of HSC were also analyzed, such as compressive strength (fCM), modulus of elasticity (ECM), splitting‐tensile strength (fCTM), and modulus of rupture (fCRM). The results revealed that the damaging effect of WSF on the RCP resistance of HSC is probably due to the high conductivity of steel fibers. However, test results of CPD showed that WSF produced insignificant changes in chloride permeability of HSC. Furthermore, when made with FA, WSF‐reinforced HSC yielded very low chloride permeability. Both WSF and FA contributed to the improvement in the AAR of HSC. WSF was highly useful to tensile properties while it showed minor effects on compressive properties (fCM and ECM). Optimum ductility and durability can be achieved with HSC incorporating 1% WSF and 10%–15% FA.

Investigation of Mechanical Properties of AA7075 Alloys Aged by Various Heat Treatments

In this study, annealing (O), artificial aging (T6), retro-regression aging (RRA) and high temperature pre-precipitation (HTPP) heat treatments were applied to AA7075 aluminium alloys. The effects of these treatments on the mechanical properties of AA7075 alloy were investigated. The microstructures of the samples were examined by Optical Microscope (OM), Scanning Electron Microscope (SEM) and Energy Dispersive X-ray (EDX) analysis. Then, X-ray diffraction analysis (XRD) was conducted to identify intermetallics formed in the microstructure of the samples. Tensile and hardness tests were carried out to investigate the mechanical properties. Results showed that secondary phase particles such as Al2Cu, Al2CuMg and MgZn2 are formed in the microstructures. In terms of the mechanical properties, T6 applied samples showed the best results. The HTPP applied alloy which presented optimum ductility behaviour among the other heat-treated samples. Dimples and some cleavage surfaces were observed on the fracture surfaces of the samples. Therefore, it is concluded that a ductile/semi-ductile fracture occurred on the samples.

Optimization of post weld heat treatment cycle of fiber laser welded bainitic steel

Automobile industry has always been in look out for advanced materials that would account for greater crash resistance, high fatigue strength, optimum ductility and longer service life despite heavy mechanical loads applied on these engine components. These critical requirements are met through maintaining the complex microstructures and optimum phase constituents. The retention of microstructural constituents has always been a key parameter while fabricating these advanced automobile materials by fusion welding process. Carbide free bainitic steels are emerging out to be the candidate materials for automobile applications. Owing to their microstructure consisting fine bainitic ferrite laths that are interwoven with retained austenite in their lath boundaries. The fine Bainitic laths provide enough strength and the retained austenite phase facilitates the desired ductility. The current paper critically discusses the microstructural and microhardness variation across the zones during Fiber Laser welding of bainitic steel sheets. Keeping the phase transformations during welding in view, post weld heat treatments were undertaken. The welded steel was austenitized at 820 OC, rapidly cooled to 390 OC, and soaked at different durations before furnace cooing. The microstructure variation and microhardness profiling were done at all these heat treatment conditions. Basing on the analyses, the heat treatment cycle has been optimized.

Effect of fiber type and content on the flexural behavior of high strength concrete beams with low reinforcement ratios

The effect of fiber types and fractions on the flexural behaviors of High Strength Concrete (HSC) beams with minimum reinforcement ratios were investigated experimentally. The main parameters in the conducted study were fiber type, the volume fraction of fiber and axial reinforcement ratio. Therefore, totally eighteen beam specimens containing both fiber reinforced concrete (RC) and conventional concrete were tested to examine pure bending regions of beams using four-point loading method. Three aspects were analyzed: (i) cracking, yielding and ultimate flexural loads, (ii) variation of the neutral axis depth and (iii) minimum reinforcement ratio required to sufficient ductility. Test results indicate that increase in the volume fraction of the steel fiber significantly improves the yielding load level of HSC beams, while addition of carbon fiber has a trivial effect on that load. Increasing the volume fraction of steel and carbon fiber causes the decline of the flexural ductility of HSC beams with low reinforcement ratio and makes the behavior of the beams more brittle in an interesting manner. Therefore, an optimum ductility number based on fracture mechanics principles was evaluated experimentally to determine the minimum reinforcement ratio supplying sufficient ductility for HSC with steel fibers.

Comparison of machinability of manganese alloyed austempered ductile iron produced using conventional and two step austempering processes

Austempered Ductile Iron (ADI) is a revolutionary material with high strength and hardness combined with optimum ductility and toughness. The discovery of two step austempering process has lead to the superior combination of all the mechanical properties. However, because of the high strength and hardness of ADI, there is a concern regarding its machinability. In the present study, machinability of ADI produced using conventional and two step heat treatment processes is assessed using tool life and the surface roughness. Speed, feed and depth of cut are considered as the machining parameters in the dry turning operation. The machinability results along with the mechanical properties are compared for ADI produced using both conventional and two step austempering processes. The results have shown that two step austempering process has produced better toughness with good hardness and strength without sacrificing ductility. Addition of 0.64 wt% manganese did not cause any detrimental effect on the machinability of ADI, both in conventional and two step processes. Marginal improvement in tool life and surface roughness were observed in two step process compared to that with conventional process.

SIFAT MATERIAL POLYESTER HYBRID COMPOSITE - BATANG BEMBAN (Donax Canniformis)

Bemban (Donax Canniformis) is a plant similar to rattan, the stem produces fiber woven material. This plant has other names bamban, bumban, bomban, and so forth. Composites are a new type of material combined with two or more ingredients and have different properties with each other both physical properties and chemical properties. From the research of this hybrid composite stem rod, it is known in the specimens of impact test of volume fraction 60% bemban (Energy Absorption 21,11 J and Impact Price 0,0332 J / mm²) has the most optimum ductility than volume fraction 40% Energy Absorption 20.62 J and Impact Price 0.0324 J / mm²) and 50% bemban bemban (Energy Absorption 20,96 J and Impact Price 0.0330 J / mm²). In bending test specimens, the volume fraction of 60% bemban stem (Bending Strength 0.45 MPa) has the most optimum ductility properties compared to the volume fraction of 40% bemban rod (Bending Strength 0.63 MPa) and 50% bemban (Bending Strength 0.72 MPa). In tensile specimens fraction volume of 60% bemban rod (Tensile Strength 0.00449 MPa) has the most optimum ductility properties compared to volume fraction of 40% bemban rod (Tensile Strength 0.00224 MPa) and 50% bemban rod (Pull Strength 0.00284 MPa).

Microstructural Evolutions and Properties of Partially Austenitizing and Austempered Ductile Irons

In this study, commercial FCD700 ductile irons are austenitized in the intercritical region to observe their effects upon the microstructures and mechanical properties of austempered ductile irons (ADIs). The austenitizing temperature is chosen such that ferrite, austensite, and graphite coexist in the microstructures. Strength of 974 MPa, 16.4% elongation, and impact energy of 166 J are achieved by the ADI austenitized at 1103 K and subsequently austemperted at 673 K. These properties are in contrast to 790 MPa strength, 8.2% elongation, and 42 J impact energy in as-cast FCD700. The properties are also superior to the traditionally austempered ductile iron with 967 MPa strength, 12.7% elongation, and 124 J impact energy. Combinations of the optimum ductility and strength are achieved by 8–19% of proeutectoid ferrite and over 20% of retained austenite in the intercritically treated microstructures. Nanoscale twinned and lenticular martensite forms within the micro-size blocky retained austentite islands during plastic deformation leading to the transformation induced plasticity. The intercritically austenitizing and austempering treatments provide unique combination of strength and elongation for commercial ductile irons.

Improving microstructure and ductility in the Mg–Zn alloy system by combinational Ce–Ca microalloying

A strategy is proposed to enhance the microstructure and mechanical properties of Mg–Zn alloys by combining microalloying additions of the rare earth element Ce and the non-rare earth element Ca. The double additions of Ce–Ca are found to significantly increase tensile elongation compared to binary Mg–Zn, or single additions of either Ce or Ca. Microstructure analysis reveals that the Ce–Ca additions increase ductility by modifying texture and refining grain size. Texture modification is attributed to solute effects from the microalloying elements, particularly Ca, while grain refinement is additionally influenced by a fine dispersion of Mg6Ca2Zn3 precipitates that form during rolling and pin grain boundaries. The microalloying element additions also lead to large secondary phase particles in the alloys, which can limit ductility enhancement by promoting early fracture. By scaling Zn content in the Mg–Zn–Ce–Ca alloys, the Mg6Ca2Zn3 phase fraction and Zn solute content can be controlled for optimum ductility or strengthening potential.

Influence of Experimental Environment on the Enhancement of Ultra Fine Grain Structure with Optimum Ductility of Equal Channel Angular Pressed Copper

Strengthening the engineering material through Severe Plastic Deformation and associated structural refinement is an established practice. Among the Severe Plastic Deformation process, Equal Channel Angular Pressing (ECAP) assumes a significant place. In this, it is possible to attain even ultra fine grain (UFG) structure through high deformation in bulk material working mode. However ECAPed material suffers lack of ductility, structural inhomogenity and even thermodynamically unstable structure, as evidenced in the published literature on ECAP of copper. The present study on ECAP of commercial purity copper aimed to attain a structure of higher hardness by shedding little ductility is deviated from the past work; in this, commercial quality copper is ECAPed at 3000 C with a die geometry channel angle of 1100 and corner angle of 200 necessitating less local/working stress. During certain number of passes (six passes), the material experiences higher hardness with fair amount of ductility. The material does not exhibit any further strengthening beyond six passes, which is possibly due to dislocations annihilation/recovery. The increased strength and loss of ductility of the material results in degrading the material when it undergoes tenth pass.

Optimum Ductility Assessment of Earthquake Resistant Structures

Provision of ductility in the structures according to the modern design codes lead to more economic constructions, while safety levels reach higher rates. The philosophy is based into allowing some damage to occur in predetermined elements where enough ductility has been provided in order to ensure the member’s capacity during an earthquake. This research focuses on investigating optimum ductility provisions for buildings to achieve the desired performance. The aim is to assess the parameters which affect ductility demands and overall present a comprehensive methodology for evaluating the structural performance. Analytical work was based on the comparison of two 4-storey reinforced concrete buildings designed as high ductility class (DCH) and medium ductility class (DCM) upon a strong rock (Ground type A, Eurocode 8 soil classification)according to the Eurocode 8. For a fair comparison both buildings were designed to have same vibration frequencies in order to experience same energy release rates under a number of earthquakes with varied ground acceleration amplitudes and frequency spectrums. The main criteria for the comparison were: (i) the inter-storey drifts, (ii) the energy distribution among the floors, (iii) the structural damage in terms of plastic hinges initiation and ductility demand rates, (iv) total energy dissipation and (v) top floor displacements. The damage rates in the structures were found to be directly correlated to the earthquake’s frequency range. Low frequency seismic events corresponding to high periods in the elastic response spectrum used for the design of the structures were more catastrophic. The paper proved that DCH buildings perform generally better than DCM for high ground acceleration amplitudes, while for smaller GAA where the responses are governed by the stiffness in the elastic response range the DCM structures have functional superiority. Higher ductility provisions have been found beneficial for the structural performance, especially for higher ductility demands caused by higher intensity earthquakes with increased return periods and ground acceleration amplitudes.

A new ductility model of reinforced concrete beams strengthened using Fiber Reinforced Polymer reinforcement

Despite the superior performance of Fiber Reinforced Polymer (FRP) as compared with conventional steel bars in terms of high strength-to-weight ratio, corrosion resistance, and high fatigue performance, FRP strengthened beams exhibit lower ductility due to the linear elastic response of the FRP reinforcement. Several ductility and deformability models were developed in order to account for the elastic behavior, i.e. high elastic energy, of FRP when used for strengthening existing steel reinforced concrete or for new construction. In this paper, a new ductility expression that relates the deformability of a reinforced concrete (RC) structure strengthened using FRP to the energy dissipated, was developed. The developed expression also considers the type of loading, static or fatigue. The new expression was validated against experimental test results of RC beams strengthened using prestressed Near Surface Mounted (NSM) carbon FRP un-fatigued and fatigued beams. Furthermore, the ductility index at which the deformability of the structure equals the ratio of total energy dissipated to elastic energy, defined as the optimum ductility index, was investigated for both the un-fatigued and fatigued beams. The prestress strain corresponding to the optimum ductility index was found to be 2830με (the strain value can be determined using an accepted arbitrary test such as monotonic test) while no optimum ductility was achieved for the case of the un-fatigued beams. It is noteworthy that the optimum ductility index is subject to the variability of design, beam geometry, and prestressing level. Therefore, the ductility evaluation of the NSM CFRP strengthened beams was meant to give only an insight into the problem and not to propose certain limits.

Effect of Heat Treatment on Microstructure and Mechanical Properties of TRIP Steel Sheets Containing Aluminium

Effect of heat treatment on microstructure of TRIP steel sheets containing aluminium was investigated on Gleeble 3500 thermal simulation testing machine. The microstructure evolution with variation of time and temperature was measured by means of optical metallography (OM) and X-ray stress analyzer. The tensile properties of TRIP steel at room temperature were also measured. It was shown that the maxium value of product of strength and ductility of 22858 MPa% was obtained by treatment of intercritical annealing temperature at 800 for 3 mins and bainitic holding temperature at 400 for 6 mins. The value of yield strength was mainly determinated by the volume fraction of bainite and the content of retained austenite was the key factor to result in optimum strength and ductility of TRIP steel. In addition, the properties of TRIP steel were markedly decreased because martensite, which was deleterious to the ductility, was present in microstructure of the steel soaking at bainitic temperature 350。C for 6 mins.